The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly includes at least one head, typically several, for reading and writing data from and to the disk. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The head stack assembly includes an actuator assembly, at least one head gimbal assembly, and a flex circuit assembly. A conventional “rotary” or “swing-type” actuator assembly typically includes a rotary actuator having an actuator body. The actuator body has a bore and a pivot bearing cartridge engaged within the bore to facilitate rotational movement of the actuator assembly between limited positions about an axis of rotation. A coil support extends from one side of the actuator body. An actuator coil is supported by the coil support and is configured to interact with one or more permanent magnetic elements, typically a pair, to form a voice coil motor. One or more actuator arms extend from an opposite side of the actuator body. Each head gimbal assembly includes a head that typically includes a transducer for writing and reading data and that is distally attached to each of the actuator arms. Each transducer typically includes a writer and a read element. The transducer's writer can be of a longitudinal or perpendicular design, and the read element of the transducer may be inductive or magnetoresistive. Each magnetic disk includes opposing disk surfaces. Data may be recorded along data annular regions on a single disk surface or both. As such, the head stack assembly may be pivoted such that each head is disposed adjacent to the various data annular regions from adjacent to the outer diameter to the inner diameter of each disk.
The spindle motor typically includes a spindle motor base, a spindle motor shaft, a rotatable spindle motor hub, a stator disposed at the disk drive base, a magnet attached to an underside of the spindle motor hub, and a bearing cartridge disposed between the spindle motor shaft and the spindle motor hub to facilitate rotational attachment of the spindle motor hub to the spindle motor base. The spindle motor hub may include an outer flange which is used to support one or more of the disks. The disks may be separated by disk spacers. A disk clamp and disk clamp screws may be used to secure the disks to the spindle motor hub. The various rotating elements associated with the disks may be referred to as a disk pack.
The stator typically includes a series of coils and is concentrically positioned about the spindle motor shaft, adjacent the spindle motor hub. The coils are in electrical communication with the printed circuit board assembly. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet otherwise associated with the spindle motor hub, thereby imparting a rotational motion onto the spindle motor hub. Rotation of the spindle motor hub results in the rotation of the overall disk pack including the attached disks.
A topic of concern is rotational balancing of the spindle motor and the overall disk pack. It is important that the mass of the disk pack be balanced so as to reduce dynamic vibrations during operation of the disk drive. Excessive imbalance can degrade the disk drive performance not only in terms of read/write errors, but also in terms of seek times. Excessive imbalance may result in an undesirable acoustic signature and may even result in damage or excessive wear to various disk drive components.
Accordingly, there is a need in the art for an improved configuration and method for balancing of the spindle motor and/or the overall disk pack.